The present invention relates generally to washing machines and more particularly to a brake system for a washing machine or other appliance that can adapt to the size of the load held within the machine.
Vertical axis washing machines include a wash basket that spins about a vertical axis. Horizontal axis washing machines include a wash basket that spins about a horizontal axis. Other washer constructions have a tilted axis between vertical and horizontal. During a spin cycle following a rinse cycle, the wash basket spins at a fairly high rate of speed in order to extract water from the clothing that has been rinsed. Conventional vertical axis washing machines typically spin at a rate of about 600 to 650 revolutions per minute (RPM) or more.
Underwriters Laboratories (UL) require that, when a washing machine lid is opened during the spin portion of a cycle, the basket must stop spinning within 7 seconds. A brake mechanism is therefore required in order to slow down the rapidly spinning basket within this 7 second time interval. For conventional vertical axis washing machines, the brake mechanism typically applies the same braking pressure to the wash basket at any speed and for any wash basket load. This static or standard brake pressure has been satisfactory for the slower spin rate of these conventional machines.
However, new generations of washing machines are on the horizon that can spin the wash basket during a rinse cycle at much greater speeds, such as on the order of about 800 or greater RPM. The load required to slow and stop the wash basket within the 7 second interval is much greater at these higher rotational speeds. However, when a high braking load is applied to a wash basket that is spinning at this much higher rate and that contains a very light laundry load it produces undesirable consequences. For example, if a light load is held within the basket spinning at about 500 RPM, when the heavy brake load is applied, the washing machine components begin to vibrate and begin to cause significant noise, vibration and even movement or walking of the machine. At a minimum such conditions are unpleasant and could potentially cause more serious consequences.
Where a washing machine brake is incapable of meeting this 7 second requirement, a lid lock must be employed to prevent access to the wash drum until it has stopped spinning. Such a lid lock adds expense to the machine and creates a significant inconvenience to users.
In light of the above noted problems, it is an object of the present invention to provide a washer brake mechanism that applies sufficient brake torque for these relatively high RPM machines, but not the same brake torque under all washer conditions. It is another object of the present invention to provide a brake mechanism that does not produce a constant high brake torque that would be sufficient to brake a fully loaded basket of wet laundry and yet which would overpower a lightly loaded basket. It is a further object of the present invention to provide a washer brake mechanism that produces a variable brake torque sufficient for different laundry loads. It is yet another object of the present invention to provide a washer brake mechanism that applies a brake torque that is variable according to particular laundry basket conditions. It is another object of the present invention to provide a load adaptive washer brake mechanism that automatically adjusts the applied brake torque according to the mass of the load held within the wash basket and the rotational speed of the basket.
It is another object of the invention to provide a load adaptive brake system for an appliance in which a drive motor and the rotatable vessel are selectively coupled and uncoupled and a braking mechanism is selectively engaged and disengaged as the uncoupling and coupling occurs, respectively. It is a still further object of the invention to use the reactive force of the motor to disengage the braking mechanism if the rotating vessel is being slowed too quickly by the braking mechanism. A preferred embodiment of the invention is in a vertical axis washer, although the invention can also be used in horizontal and tilted axis washers as well as other appliances having a rotatable vessel.
These and other objects, features and advantages of the present invention are provided by a load adaptive brake system for an appliance according to the present invention. In one embodiment, the load adaptive brake system includes a stationary brake drum supported by the washing machine. The brake system also includes a brake plate and a pair of opposed brake shoes supported by the brake plate and including brake linings facing the brake drum. A spring is interposed between first ends of the brake shoes for forcing the brake pads against the brake drum. A cam is slidably carried on a rotary shaft of the washing machine and has a pair of cam surfaces. A roller is disposed on a second end of each of the brake shoes. Each roller bears against one of the cam surfaces of the cam. The cam surfaces each have a profile so that the cam will rotate to at least partly relieve brake pressure on the brake drum as the motor of the washing machine decelerates and applies residual deceleration torque through the motor armature to the cam if the motor is caused to decelerate faster than the normal uncoupled deceleration rate. That is, the motor has a normal deceleration rate when the motor is not coupled to the wash basket. This normal deceleration rate, in a preferred embodiment, is such that the motor would decelerate from full speed, at which the wash basket is rotating at least 500 rpm, and perhaps at 800 or greater rpm, to a stop condition in about 5xc2xd-6xc2xd seconds.
The brake system was developed to be able to apply sufficient brake torque to stop a fully loaded wash basket from a full speed spin to a stopped condition in less than 7 seconds. When this same brake torque is applied to an empty wash basket, the basket is slowed from full speed to a stopped condition in about 2 seconds. While such a speed is well within the time requirements, such abrupt braking causes the entire washing machine to jerk and move about. If, however, the motor is coupled to the empty wash basket as the wash basket is being slowed down, the motor is caused to slow down faster than its normal deceleration speed, resulting in a reaction torque being developed by the motor and transmitted back to the cam, rotating the cam in a reverse direction to release the braking pressure of the brake pads against the brake drum. This causes a reduction in the net brake torque, thereby lengthening the time for the wash basket to come to a complete halt, would also prevent the machine from jerking and moving about. Since the motor naturally stops in less than 7 seconds, coupling the motor with the basket does not cause the coupled combination to stop in greater than 7 seconds because the reaction torque lessens as the stoppage rate approaches 5xc2xd to 6xc2xd seconds, and the lesser reaction torque becomes insufficient to overcome the strength of the spring through the cam, hence reapplying the brakes.
Thus, in a preferred embodiment, a mechanism is provided to automatically couple the basket to the motor if the basket is being slowed faster than the normal deceleration rate of the motor and to uncouple the motor from the basket if the basket is being slowed slower than the normal deceleration rate of the motor. The profile of the cam is selected such that the reaction torque enables the brakes to be at least partially released through rotation of the cam.
In another embodiment of the invention, a vertical axis washing machine includes a wash basket that is rotatable about a generally vertical axis. A rotary shaft is coupled to the wash basket and a motor is coupled to the rotary shaft for rotating the wash basket. A brake drum is stationary and supported by a portion of the washing machine. A brake plate supports a pair of brake shoes wherein the brake plate is carried by a portion of the rotary shaft of the washing machine and rotates relative thereto. A pair of brake shoes are supported by the brake plate wherein each brake shoe has a brake lining that can bear against the brake drum. A spring is interposed between first ends of the brake shoes that forces the brake linings against the brake drum. A cam is slidably carried on a portion of the rotary shaft and has a pair of cam surfaces. A pair of cam rollers are supported by respective second ends of the brake shoes. Each cam roller bears against a respective one of the cam surfaces of the cam. Each cam surface has a profile that is adapted to at least partly reduce the amount of brake pressure applied by the brake linings against the drum upon rapid deceleration of the motor through residual torques applied through the motor armature during rapid deceleration.
In another embodiment a load adaptive brake system is provided for an appliance which includes a motor, a drive wheel driven by the motor and a rotatable vessel. A brake surface is fixed relative to a non-movable portion of the appliance and at least one brake shoe carried by the vessel to rotate with the vessel. A biasing mechanism is engageable with the brake shoe to press the brake shoe into engagement with the brake surface. A cam is carried on the vessel, but is rotatable with respect thereto, and engageable with a portion of the brake shoe to overcome a bias of the biasing mechanism when the cam is rotated relative to the vessel in a first direction to disengage the brake shoe from the brake surface. A coupling mechanism is arranged between the drive wheel and the cam to selectively couple the motor to the vessel by rotation of the cam in the first direction when the drive wheel is rotating in one direction relative to the cam and to uncouple the motor from the basket when the drive wheel is rotating in a second, opposite direction relative to the cam.
These and other objects, features, and advantages of the present invention will become apparent upon a reading of the detailed description and a review of the accompanying drawings. Specific embodiments of the present invention are described herein. The present invention is not intended to be limited to only these embodiments. Changes and modifications can be made to the described embodiments and yet fall within the scope of the present invention.